I. Field of the Invention
This invention relates to bearings for rotary cone rock bits. More particularly, this invention relates to spindle bearings for sealed bearing rotary cone rock bits.
II. Description of the Prior Art
It is common practice to hardface the spindle or pilot bearing on both its axial and thrust surfaces. The pilot bearing extends from the main journal bearing supporting the rotary cone rotatively retained thereon. Typically, the spindle is subsequently ground or turned to finish geometry. The mating bore and thrust face formed in the cone are made from carburized steel, and are ground or turned to finish geometry after carburizing and quenching.
It is also state of the art to utilize only the thrust surface formed between the main journal bearing and the spindle, the end of the spindle bore in the cone being spaced from the spindle thrust face to prevent contact therebetween.
All of the foregoing prior art designs use a hard vs. hard material pair formed between the spindle and the cone bore resulting in a high friction coefficients between the bearing surfaces. This arrangement also does not conform easily to accommodate slight misalignments. This usually results in edge loading and high friction.
U.S. Pat. No. 4,270,812 assigned to the same assignee as the present invention, teaches a cylindrical bearing sleeve metallurgically bonded to a spindle bearing with a thrust disc bonded to the end of the pilot bearing. The bearing sleeve and disc would, however, suffer from edge loading and high friction as heretofore mentioned.
U.S. Pat. No. 4,875,532 describes a one piece radial and thrust bearing that is held by interference fit in the cone spindle bore. The thrust surface formed between the main bearing and the spindle is the primary bearing. This bearing is limited to a single wear surface and does not accommodate for possible misalignment nor does the bearing make use of the end thrust surface of the spindle bearing.
The spindle cap bearing of the present invention with its floating geometry teaches dual wear surfaces on the thrust and radial bearing surfaces and is more accommodating to misalignment due to its inherent flexibility. The relatively soft floating bearing deforms easily to reduce high stresses due to the aforementioned misalignment. Moreover, the floating member has a higher rotational speed capability than the existing prior art.